Commentary for Leviticus 21:23

אך אל הפרכת ONLY [HE SHALL NOT GO IN] UNTO THE PARTITION VEIL for the purpose of applying the seven sprinklings which are to be made upon the partition vail (cf. Leviticus 16:17).

To sprinkle seven sprinklings. Because if not so, what has he to do with the Curtain that the verse should warn him from entering there.

אך אל הפרוכת לא יבא, “but he must not go beyond the dividing curtain;” Torat Kohanim demonstrates why the additional mention of the altar in this verse was necessary by stating that if the Torah had only mentioned the dividing curtain, we might have thought that seeing that anything beyond was the Holy of Holies, anyone who was not a priest was forbidden to enter there, and if it had written only that the altar was out of bounds to them that the reason was that they were not allowed to perform sacrificial rituals. By mentioning both the dividing curtain and the altar situated in the Sanctuary, no one could make such an error.